Dosage-dispensing devices of this kind find application in particular for the dispensing of small quantities of, e.g., toxic substances with high precision into small target containers. In many cases, such target containers are set on a balance which serves to weigh the substance quantity delivered from the dosage-dispensing device, so that it can subsequently be processed further in accordance with a set purpose.
The substance to be dispensed is contained for example in a source container which is equipped with a dispensing head. It is desirable to discharge the dosage material through a small opening of the dosage-dispensing device, so that it can be filled in a targeted stream into a container with a narrow fill opening.
Dosage-dispensing devices for dry and/or pulverous bulk materials, for example for pigments in powder form, belong to the known state of the art and are in practical use. As an example, a dosage-dispensing device is described in U.S. Pat. No. 5,145,009 A, which consists of a source container with a closable outlet at its underside. The function of a closure element is performed by a cone-shaped valve body whose diameter decreases in the upward direction, which can be moved vertically downward in order to open an outlet opening, which rotates while in its open position and is equipped with means for advancing the material in the direction of the outlet opening. The source container is further traversed by a closure shaft which protrudes from the top of the source container and can be coupled to a drive mechanism. The source container is connected at its underside to the dosage-dispensing device by way of an attachment flange. Several pressure cylinders are arranged to act on the lid of the source container, wherein the outlet opening and thus the delivery quantity from the source container can be influenced by way of the piston stroke. If strongly coagulating powders or substances in paste form are to be dispensed, it is of extraordinary importance for the closure shaft to be arranged in a vertical position, because the material flow in the container occurs in the vertical direction and is thus being assisted by the force of gravity.
For refilling, the dispensing head and source container can be removed together from the drive mechanism. However, due to the drive shaft being arranged in the source container, the refilling operation proves to be quite difficult, particularly when the materials being refilled are toxic substances or substances used for pharmaceutical preparations, where a contamination could represent a danger for the consumers of the pharmaceutical product.
As a way of countering this problem, a dosage-dispensing device is disclosed in EP 0 234 332 A1 which has a source container to whose underside a dispensing head is connected and to whose topside a drive mechanism is coupled. The source container further has a laterally protruding filler neck through which the source container can be filled. In this dosage-dispensing device, too, the drive shaft is arranged inside the source container.
The most serious problem area in the two foregoing solutions lies in the bearing- and passage area of the drive shaft. If dosage material enters into the bearing- and passage area, a dosage material with very hard particles can cause serious wear in the bearing. This can lead to a blockage of the drive shaft, and the abrasive wear creates the danger that abraded matter could contaminate the dosage material or that the precise operation of the dispensing head is compromised by an increasing amount of play in the bearing. A blockage of the drive shaft is particularly dangerous if it occurs in the opened state and the dosage material can pour out of the dispensing head into the surrounding area in an uncontrolled manner. Soft powders can be ground up to an ultra-fine consistency in the bearing and can escape uncontrollably through the bearing- and passage area to the outside and contaminate the environment.
In order to prevent the closure shaft from becoming blocked in the bearing- and passage area due to dosage material entering into the bearing, the bearing- and passage area in state-of-the-art solutions is arranged as far away as possible from the highest possible powder fill level. Further according to the state of the art, a variety of polymer sealing means are being considered for a protective seal. The limit for the powder fill level in devices with a lateral filler neck is determined by the location where the neck meets the container. These solutions result in a large overall height of the dosage-dispensing heads, which leads to a considerable overall height of the dosage-dispensing device and, accordingly, to instruments that are very expensive and unwieldy. Furthermore, elastic sealing means are very susceptible to erosion, can be attacked by solvents contained in the dosage material, and are therefore hardly a suitable choice for durable seals of a bearing- and passage area in which a drive shaft is supported in rotary and translatory movement.
In view of the problems of the dosage-dispensing devices and dispensing heads of the foregoing description, the present invention therefore has the objective to provide a dispensing head, or a dosage-dispensing device equipped with a least one such dispensing head, from which dosage material can be dispensed without the risk that the environment and/or the dosage material could become contaminated due to penetration of dosage material into the bearing- and passage area. A further objective of the invention is to provide a simple way in which the source container and the dispensing head together as a closed unit can be set into the drive mechanism as well as separated again from the latter after their contents have been dispensed.